Apparatus for stamping and forming sheet metal moving along a movement path in the past, has employed flying dies, moving along rails, on either side of the sheet metal. Other forms of moving die apparatus have employed dies mounted on a rotary core, with the dies moving around a more or less circular path.
The rotary moving die apparatus is of complex design, and requires great precision in the control of movement. Flying dies moving to and fro on rails, are easier to design and build and control, because the movement of the die is linear instead of rotary. The rotary type of moving die apparatus seems to offer some advantages in that the rotation of the rotors carrying the dies is continuous in one direction. By contrast the movement of flying dies moving on rails is necessarily a reciprocation, from forward to stop to reverse to stop to forward and so on. One of the problems in the design of flying dies moving on rails, is that the dies, and their associated die plates and movement mechanism represents a fairly heavy mass of metal, and that entire mass must be accelerated from zero, to the line speed of the sheet metal and then stopped, reversed and reaccelerated again. In one highly successful form of flying shear, designed by the present inventor, the acceleration was achieved by a pneumatic cylinder and the reverse movement was achieved by a gear and a rack system.
It has now been found that in the flying die system, the forward and reverse movement can advantageously achieved through a continuously rotating crank. This form of movement reduces the mass of metal parts which must be starting and stopping, since the movement is achieved through a continuously rotating crank. With this improvement, the flying dies can be operated at a much higher line speed, enabling the running of the complete sheet metal production line at a greater efficiency.